1. Field of the Invention
The present invention relates generally to methods and apparatus for treating disorders by using cranial nerve stimulation. More particularly, it concerns methods and apparatus for treating eating disorders, such as bulimia, by using vagus nerve stimulation.
2. Description of the Related Art
The human nervous system (HNS) includes the brain and the spinal cord, collectively known as the central nervous system (CNS). The central nervous system comprises nerve fibers. The network of nerves in the remaining portions of the human body forms the peripheral nervous system (PNS). Some peripheral nerves, known as cranial nerves, connect directly to the brain to control various brain functions, such as vision, eye movement, hearing, facial movement, and feeling. Another system of peripheral nerves, known as the autonomic nervous system (ANS), controls blood vessel diameter, intestinal movements, and actions of many internal organs. Autonomic functions include blood pressure, body temperature, heartbeat and essentially all the unconscious activities that occur without voluntary control.
Like the rest of the human nervous system, nerve signals travel up and down the peripheral nerves, which link the brain to the rest of the human body. Nerve tracts or pathways, in the brain and the peripheral nerves are sheathed in a covering called myelin. The myelin sheath insulates electrical pulses traveling along the nerves. A nerve bundle may comprise up to 100,000 or more individual nerve fibers of different types, including larger diameter A and B fibers which comprise a myelin sheath and C fibers which have a much smaller diameter and are unmyelinated. Different types of nerve fibers, among other things, comprise different sizes, conduction velocities, stimulation thresholds, and myelination status (i.e., myelinated or unmyelinated).
Gastrointestinal functions are controlled by various cranial nerves that traverse portions of the human body. For example, cranial nerve X (i.e., the vagus nerve) traverses the esophagus and the stomach. Below the roots of the lungs, the vagus nerve diverges into various parts, which innervate the esophagus region. Traversing the esophagus downward, the vagus nerve divides and reunites to form open meshed formations known as the esophageal plexus. The esophageal plexus contains small ganglia. Much of the branches of the right vagus nerve incline posteriorly while most of the left vagus nerves incline anteriorly. The esophageal plexus also includes thoracic portions of the sympathetic nerve trunks, e.g., the thoracic splanchnic nerves. Below the esophageal plexus, the vagus nerve traverses to form the gastric branches of the anterior and the posterior vagus trunks.
There are various disorders relating to the gastrointestinal system, including various gastrointestinal-related and eating diseases. Motility disorder is a gastrointestinal disorder that the causes muscular contractions of the esophagus that guide food to the stomach to become dis-coordinated or weak. This interferes with movement of food and fluid down the esophagus. Other eating disorders include anorexia nervosa, which is a disorder that is characterized by the restriction of food and the refusal to maintain a minimal normal body weight. Another eating disorder is bulimia nervosa, which is characterized by addictive binge-purge cycles. A bulimic person eats compulsively and then purges through self-induced vomiting or involuntary vomiting.
Yet another disorder/eating disorder includes compulsive overeating, which is characterized by vicious cycles of binge eating and depression. Another gastrointestinal or eating disorder includes binge overeating. In the case of binge overeating, nerve signals indicative of the fact that a person is full may not register in the brain. Various age-groups of people are affected by eating disorders and other gastrointestinal disorders. Treatments to address these disorders include physiological treatments, such as drug treatments, as well as psychological treatments, such as counseling. Besides drug regimens, invasive medical procedures, and/or counseling, effective treatment of such diseases and disorders are fairly limited. Further, certain patients may not react favorably to various types of drugs or other treatments.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.